MIT-bred technology would let cars help each other avoid traffic jams

If you get stuck in traffic a lot, your next car may be able to talk to other vehicles and help keep you off jammed roads.

Researchers at the Massachusetts Institute of Technology used virtual tokens, cellphones and vehicle-to-vehicle wireless LANs to build a system for allocating the limited space available on major thoroughfares. It doesn't require any physical infrastructure, such as tollbooths, so it could be implemented quickly almost anywhere, they said.

Instead of using cameras or electronic tollbooths by the roadway to detect cars passing a certain point, the MIT system, called RoadRunner, is based on GPS (Global Positioning System) information from the driver's cellphone in each car. As more cars get connected to the Internet, the system may be able to go into the car itself, according to Jason Gao, a graduate student in electrical engineering and computer science who developed the system with Professor Li-Shiuan Peh.

RoadRunner is designed to solve the problem of congested roads, with or without a government charging tolls for driving in crowded areas during rush hour. Once it detects that a particular route is crowded, RoadRunner generates driving directions to approaching cars that recommend a different way to go.

At the heart of RoadRunner is a limited set of tokens that the system assigns to vehicles within the affected area. When the road isn't crowded, every driver entering the zone receives a token, but as it fills up, later arrivals get the alternate driving directions instead. There's nothing to stop a car from crossing the line without a token, but that action could trigger a fine if law enforcement wanted to impose one.

The system doesn't track the precise location of each car. Instead, the server only registers whether a car is inside or outside the congestion zone and whether it has a token.

To speed up the sharing of tokens, RoadRunner takes advantage of IEEE 802.11p, a vehicle-to-vehicle (V2V) variant of the technology behind Wi-Fi. Initially, a server generates the tokens and distributes them to cars via cellular, but after that, the cars can pass them directly to one another via 802.11p, Gao said in an email interview. The V2V network can transfer tokens faster because it has lower latency than cellular, and using it cuts down on cell traffic, Gao said.

IEEE 802.11p is starting to emerge as a key technology for self-driving vehicles and for semi-autonomous safety networks that may precede cars that drive all by themselves. Among other things, it's being used for proximity warning systems that let one vehicle tell another when it's entering an intersection. If two cars are approaching that intersection at full speed, such as at a blind intersection, the V2V network can send an alert that triggers alarms to the driver in each car.

RoadRunner might be an alternative to the congestion-control system in Singapore, one of the world's most advanced, which levies different tolls based on the amount of traffic on the stretch of road that a driver is entering. Singapore's current system uses gantries, or structures built over the roadway, that communicate with transponders in each car. That means the Land Transit Authority, which operates the system, can only regulate congestion where it's built a gantry.

By contrast, RoadRunner can be set up in any area, based on GPS coordinates, and can point drivers to alternative routes to help them avoid the congested area. Gao ran simulations with RoadRunner using data from the Land Transit Authority and estimated that it would increase average car speed by 7.7 percent during peak traffic periods, over what Singapore's current toll-based system achieves. Gao and Peh also tested RoadRunner on 10 cars in Cambridge, Massachusetts, MIT's hometown.

One big step remaining for making RoadRunner a reality is implementation of 802.11p. For their real-world test in Cambridge, Gao and Peh equipped cars with commercial 802.11p radios, which are about the size of a typical dashboard transponder used for tollbooths, according to MIT. The driver's smartphone, equipped with a RoadRunner app, controlled those external radios. But Gao said 802.11p radios are already being built into some cars and he expects them to appear in smartphones, too. That would provide two different hardware platforms for using RoadRunner.

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